System and method to calculate rms current and true power in a multidrop sensor network

ABSTRACT

According to one aspect, embodiments of the invention provide a system for monitoring a plurality of circuit branches coupled to an input line, the system comprising a communication bus, a plurality of sensor circuits, each configured to be coupled to the communication bus and at least one of the plurality of circuit branches, wherein each sensor circuit is further configured to sample current in the at least one of the plurality of circuit branches, a controller configured to be coupled to the communication bus and the input line; wherein the controller is further configured to sample voltage on the input line, and wherein the controller is further configured to synchronize, via the communication bus, current sampling performed by the plurality of sensor circuits with the voltage sampling performed by the controller.

BACKGROUND OF INVENTION

1. Field of the Invention

At least one example in accordance with the present invention relatesgenerally to systems and methods for monitoring a load center forcurrent, power and energy usage.

2. Discussion of Related Art

A load center or panelboard is a component of an electrical supplysystem which divides an electrical power feed from a power line intodifferent subsidiary circuit branches. Each subsidiary circuit branchmay be connected to a different load. Thus, by dividing the electricalpower feed into subsidiary circuit branches, the load center may allow auser to individually control and monitor the current, power and energyusage of each load.

Current sensors are commonly used to monitor activity of a load center.For example, Current Transformers (CT) are commonly used to monitorcurrent, power and/or energy consumption in a subsidiary or main branchof a load center. A CT may be used to measure current in a branch byproducing a reduced current signal, proportionate to the current in thebranch, which may be further manipulated and measured. For example, a CTcoupled to a branch of a load center may produce a reduced current ACsignal, proportionate to the magnitude of AC current in the branch. Thereduced current AC signal may then either be measured directly orconverted to a DC signal and then measured. Based on the signalreceived, the level of current in the subsidiary branch may bedetermined.

SUMMARY OF THE INVENTION

Aspects in accord with the present invention are directed to a systemand method for monitoring a load center.

In one aspect the present invention features a current monitoring devicecomprising a current transformer configured to be removably coupled to apower line and to generate a reference signal having a level related toa current level of the power line, a sensor circuit connected to thecurrent transformer and configured to be removably coupled to acommunications bus and to convert the reference signal to a digitalreference signal and provide a signal indicative of the current level tothe communication bus, and a housing containing the sensor circuit andthe current transformer. In one embodiment, the sensor circuit isconfigured to receive power from the communications bus.

According to one embodiment, the housing includes a first portioncontaining the current transformer and a second portion containing thesensor circuit, and wherein the first portion is rotatably coupled tothe second portion. In one embodiment, the second portion of the housingincludes an insulation displacement connector configured to couple thesensor circuit to the communication bus. In another embodiment, thesecond portion of the housing further includes a lid configured to lockthe communication bus in place adjacent to the insulation displacementconnector.

According to one embodiment, the housing is configured to be rotatedbetween a first position and a second position, wherein, in the firstposition, the first portion of the housing is rotated away from thesecond portion to allow external access to an interior chamber, andwherein, in the second position, the first portion of the housing isrotated towards the second portion so that the housing encompasses theinterior chamber.

According to another embodiment, the sensor circuit further includes atransceiver coupled to a microcontroller and configured to receive thedigital reference signal and provide data related to the digitalreference signal to the communications bus. In one embodiment, thetransceiver is further configured to receive data from the communicationbus indicative of at least one of voltage, frequency and phaseinformation of the power line. In another embodiment, themicrocontroller is configured to calculate power parameters of the powerline using the digital reference signal and the data from thecommunications bus.

In another aspect the present invention features a method for monitoringa power line within a load center, the method comprising coupling acurrent transformer to the power line within the load center, coupling asensor circuit to a communication bus within the load center,generating, with the current transformer, a reference signal having alevel related to a current level of the power line, converting, with thesensor circuit, the reference signal to a digital reference signal, andproviding the digital reference signal to the communication bus.

According to one embodiment, the act of coupling a current transformerto the power line includes encompassing the power line within thecurrent transformer. In another embodiment, the act of coupling a sensorcircuit to a communication bus includes piercing an outer insulationlayer of the communication bus with at least one contact of the sensorcircuit and connecting the at least one contact to an appropriateconductor within the communication bus.

According to another embodiment, the method further comprises assigninga unique address to the sensor circuit over the communications bus. Inone embodiment, the act of providing includes providing the digitalreference signals to the communication bus at a time designated by anexternal controller. In another embodiment, the method further comprisesreceiving, with the sensor circuit, power from the communications bus.

In one aspect the present invention features a device for monitoringcurrent in a power line, the device comprising a current transformerconfigured to generate a reference signal having a level related to acurrent level of the power line, a sensor circuit configured to convertthe reference signal to a digital reference signal and provide datarelated to the digital reference signal to a communication bus, andmeans for containing the current transformer and the sensor circuitwithin a single housing and coupling the single housing to the powerline and the communications bus.

According to one embodiment, the sensor circuit is configured to receivepower from the communications bus. In another embodiment, the sensorcircuit includes a transceiver coupled to a microcontroller andconfigured to receive the digital reference signal and provide datarelated to the digital reference signal to the communications bus.

According to another embodiment, the transceiver is further configuredto receive data from the communication bus indicative of at least one ofvoltage, frequency and phase information of the power line. In oneembodiment, the microcontroller is configured to calculate powerparameters of the power line using the digital reference signal and thedata from the communications bus.

In one aspect the present invention features a system for monitoring aplurality of circuit branches coupled to an input line, the systemcomprising a communication bus, a plurality of sensor circuits, eachconfigured to be coupled to the communication bus and at least one ofthe plurality of circuit branches, wherein each sensor circuit isfurther configured to sample current in the at least one of theplurality of circuit branches, a controller configured to be coupled tothe communication bus and the input line, wherein the controller isfurther configured to sample voltage on the input line, and wherein thecontroller is further configured to synchronize, via the communicationbus, current sampling performed by the plurality of sensor circuits withthe voltage sampling performed by the controller.

According to one embodiment, the controller is further configured toreceive, via the communication bus, current sampling data from at leastone of the plurality of sensor circuits. In another embodiment, thecontroller is further configured to calculate at least one of RMScurrent, power, or energy usage of at least one of the plurality ofcircuit branches based on the current sampling data received from the atleast one of the plurality of sensor circuits and voltage sampling data.In one embodiment, the controller is further configured to determine aphase angle of a voltage waveform at which current sampling and voltagesampling should occur.

According to another embodiment, at least one of the plurality of sensorcircuits includes a current transformer coupled to the at least one ofthe plurality of circuit branches.

In another aspect the present invention features a method for monitoringa plurality of circuit branches coupled to a power line, the methodcomprising coupling a sensor circuit to each one of the plurality ofcircuit branches and to a communication bus, coupling a controller tothe communication bus and to the power line, sampling, with at least oneof the sensor circuits, current in at least one of the plurality ofcircuit branches, sampling, with the controller, voltage on the powerline, and synchronizing, with the controller via the communication bus,the sampling of current by the at least one of the sensor circuits andthe sampling of voltage by the controller.

According to one embodiment, the act of synchronizing comprisesdetecting, by the controller, a voltage waveform on the power line, anddetermining, with the controller, a phase angle of the voltage waveformat which the acts of sampling current and sampling voltage should occur.In one embodiment, the act of synchronizing further comprisesbroadcasting, with the controller via the communication bus, to each oneof the sensor circuits that the act of sampling current should begin,and initiating, after a predetermined delay following the act ofbroadcasting, the act of sampling voltage. In another embodiment, theact of synchronizing further comprises broadcasting, with the controllervia the communication bus, to at least one of the sensor circuits thatthe act of sampling current should begin, and initiating, after apredetermined delay following the act of broadcasting, the act ofsampling voltage.

According to another embodiment, the method further comprises receiving,with the controller via the communication bus, current sampling datafrom at least one of the sensor circuits. In one embodiment, the methodfurther comprises transmitting the current sampling data to an externalclient. In another embodiment, the method further comprises calculating,with the controller, at least one of RMS current, voltage or energyusage of at least one of the plurality of circuit branches based on thecurrent sampling data received from the at least one of the sensorcircuits and voltage sampling data.

According to one embodiment, the method further comprises transmittingthe at least one of RMS current, voltage or energy usage to an externalclient. In one embodiment, the act of transmitting includes transmittingthe at least one of RMS current, voltage or energy usage wirelessly toan external client. In another embodiment, the method further comprisesassigning, with the controller via the communication bus, uniqueaddresses to each one of the sensor circuits.

According to another embodiment, the method further comprisesconfirming, with the controller in response to the act of receivingcurrent sampling data, that the current sampling data was receivedsuccessfully, and entering, with the at least one of the sensorcircuits, in response to the act of confirming, power save mode. In oneembodiment, the act of entering power save mode comprises initiating asleep timer, wherein the at least one of the sensor circuits remains inpower save mode until expiration of the sleep timer.

In one aspect the present invention features a system for monitoring aplurality of circuit branches coupled to an input line, the systemcomprising a communication bus, a plurality of sensor circuits, eachconfigured to be coupled to the communication bus and at least one ofthe plurality of circuit branches, wherein each sensor circuit isfurther configured to sample current in the at least one of theplurality of circuit branches, a controller configured to be coupled tothe communication bus and the input line, means for synchronizingcurrent sampling performed by at least one of the plurality of sensorcircuits and voltage sampling performed by the controller.

According to one embodiment, the controller is further configured toreceive, via the communication bus, current sampling data from the atleast one of the plurality of sensor circuit. In one embodiment, thecontroller is further configured to calculate at least one of RMScurrent, power, or energy usage of at least one of the plurality ofcircuit branches based on the current sampling data received from the atleast one of the plurality of sensor circuit and voltage sampling data.

In another aspect the present invention features a system for monitoringa plurality of circuit branches coupled to an input line within a loadcenter, the system comprising a plurality of current sensors, eachconfigured to be coupled to at least one of the plurality of circuitbranches and to produce a signal having a level related to a currentlevel of the one of the plurality of circuit branches, a communicationsbus, a plurality of sensor circuits, each coupled to an associated oneof the plurality of current sensors and configured to be coupled to thecommunication bus, wherein each one of the plurality of sensor circuitsis configured to convert the signal from the associated one of theplurality of current sensors to a digital measurement signal and providethe digital measurement signal to the communication bus, and acontroller configured to be coupled to the communication bus andconfigured to receive the digital measurement signal from each sensorcircuit over the communication bus and transmit data related to thedigital measurement signal from each sensor circuit to an externalclient.

According to one embodiment, the controller is further configured to belocated within the load center. In another embodiment, the systemfurther comprises a wireless radio coupled to the controller, whereinthe wireless radio is configured to transmit the data related to thedigital measurement signal from each sensor circuit to an externalclient.

According to another embodiment, each one of the plurality of sensorcircuits is configured to be removably coupled to the communication bus.In one embodiment, each one of the plurality of current sensors isconfigured to be removably coupled to one of the plurality of circuitbranches. In another embodiment, each one of the plurality of sensorcircuits includes a secondary microcontroller coupled to the associatedone of the plurality of current sensors and configured to convert theanalog reference signal from the associated one of the plurality ofcurrent sensors to a digital measurement signal and provide the digitalmeasurement signal to the communication bus.

According to one embodiment, the controller includes a primarymicrocontroller configured to receive the digital measurement signalfrom each of the plurality of sensor circuits and provide the datarelated to the digital measurement signal from each of the plurality ofsensor circuits to the external client. In one embodiment, thecontroller further includes a power module coupled to at least one ofthe plurality of circuit branches, wherein the primary microcontrolleris further configured to measure at least one of voltage, phase andfrequency of the at least one of the plurality of circuit branches andtransmit data related to the at least one of the voltage, the phase andthe frequency to at least one of the plurality of sensor circuits viathe communication bus.

According to another embodiment, the primary microcontroller isconfigured to assign a unique address to each one of the plurality ofsensor circuits and to control communication on the communication bus.In one embodiment, the primary microcontroller is further configured tocalculate power and energy parameters of the at least one of theplurality of circuit branches based on the digital measurement signalfrom at least one sensor circuit and the measured at least one ofvoltage, phase and frequency of the at least one of the plurality ofcircuit branches

According to one embodiment, at least one secondary microcontroller isconfigured to receive the data related to the at least one of thevoltage, the phase and the frequency from the primary microcontrollerand calculate power and energy parameters of one of the plurality ofcircuit branches based on the digital measurement signal and thereceived data related to the at least one of the voltage, the phase andthe frequency.

In one aspect the present invention features a method for monitoring aplurality of circuit branches coupled to a power line within a loadcenter, the method comprising coupling a current transformer to each oneof the plurality of circuit branches, coupling a plurality of sensorcircuits to a communication bus, wherein each of the sensor circuits iscoupled to one of the current transformers, coupling a concentrator tothe communication bus, generating, in each current transformer, areference signal having a level related to a current level of one of theplurality of circuit branches, converting, with each of the plurality ofsensor circuits, a reference signal from a corresponding currenttransformer to a digital measurement signal and providing the digitalmeasurement signal to the communication bus, receiving, with theconcentrator, the digital measurement signal from each sensor circuitover the communication bus, and transmitting data related to the digitalmeasurement signal from each sensor circuit to an external client.

According to one embodiment, the method further comprises managingcommunication over the communication bus with the concentrator. In oneembodiment, the act of managing includes assigning, with theconcentrator, a unique address to each one of the plurality of sensorcircuits. In another embodiment, the act of transmitting includestransmitting the data related to the digital measurement signal fromeach sensor circuit wirelessly to an external client.

According to another embodiment, the method further comprises measuring,with the concentrator, at least one of voltage, phase and frequency ofpower provided to the plurality of circuit branches, and transmittingdata related to the at least one of the voltage, the phase and thefrequency to the plurality of sensor circuits via the communication bus.

According to one embodiment, the method further comprises calculating,with the plurality of sensor circuits, power and energy parameters ofthe plurality of circuit branches based on the received data related tothe at least one of the voltage, the phase and the frequency, providingdata related to the power and energy parameters to the concentrator viathe communication bus, and transmitting the data related to the powerand energy parameters to the external client.

In another aspect the present invention features a system for monitoringa plurality of circuit branches coupled to an input line within a loadcenter, the system comprising a plurality of current transformers, eachconfigured to be coupled to one of the plurality of circuit branches andto produce a signal having a level related to a current level of the oneof the plurality of circuit branches, a plurality of sensor circuits,each coupled to an associated one of the plurality of currenttransformers, and configured to convert the signal from the associatedone of the plurality of current transformers to a digital measurementsignal, a concentrator configured to receive the digital measurementsignals and transmit data related to the digital measurement signals toan external client, and means for providing the digital measurementsignals from the plurality of sensor circuits to the concentrator over abus.

According to one embodiment, the concentrator is further configured tobe located within the load center. According to another embodiment, thesystem further comprises a wireless radio coupled to the concentrator,wherein the wireless radio is configured to transmit the data related tothe digital measurement signals to an external client.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings are not intended to be drawn to scale. In thedrawings, each identical or nearly identical component that isillustrated in various FIGs. is represented by a like numeral. Forpurposes of clarity, not every component may be labeled in everydrawing. In the drawings:

FIG. 1 is a circuit diagram of a load center in accordance with aspectsof the present invention;

FIG. 2A is a schematic diagram of a smart CT prior to being coupled to acircuit branch in accordance with aspects of the present invention;

FIG. 2B is a schematic diagram of a smart CT after being coupled to acircuit branch in accordance with aspects of the present invention;

FIG. 3A is a schematic diagram of a smart CT prior to being coupled to acommunication bus in accordance with aspects of the present invention;

FIG. 3B is a schematic diagram of a smart CT after being coupled to acommunication bus in accordance with aspects of the present invention;

FIG. 3C is a schematic diagram of a smart CT locked together with acommunication bus in accordance with aspects of the present invention;

FIG. 4 is a circuit diagram of smart CT's coupled to a daisy chain busin accordance with aspects of the present invention;

FIG. 5 is a block diagram of a concentrator in accordance with aspectsof the present invention; and

FIG. 6 is a flow chart of a method of operation of a CT concentrator inaccordance with aspects of the present invention.

DETAILED DESCRIPTION

Embodiments of the invention are not limited to the details ofconstruction and the arrangement of components set forth in thefollowing description or illustrated in the drawings. Embodiments of theinvention are capable of being practiced or of being carried out invarious ways. Also, the phraseology and terminology used herein is forthe purpose of description and should not be regarded as limiting. Theuse of “including,” “comprising,” or “having,” “containing”,“involving”, and variations thereof herein, is meant to encompass theitems listed thereafter and equivalents thereof as well as additionalitems.

As discussed above, CT's may be utilized with a load center of anelectrical supply system to monitor circuit branches and assist inproviding efficient energy management. For instance, CT's may be coupledto circuit branches inside or outside of a load center. However,multiple challenges with CT's may arise as the electrical supply systemgrows in size and complexity.

Existing methods and systems typically rely on a system of individualCT's, each connected to a main controller and measurement unit in a “huband spoke” topology. In such a system, each CT requires dedicatedcabling connecting it to the main controller and its measurement unit,so that the number of cables or wires increases linearly with the numberof sensors. In addition, some jurisdictions have regulatory requirementson the amount of “gutter space” (i.e., space within the panelboard freeof wiring and other electronic devices) available within a panelboard.Therefore, as the number of CT's increases, the amount of cabling andcircuitry within a panelboard may become difficult to manage and violateregulatory requirements.

In some instances it may even be difficult to physically place all ofthe desired CT's and corresponding circuitry within the load center, anddue to the complexity of such a load center; installation, expansion andmaintenance may also be expensive, difficult and even hazardous.

At least some embodiments described herein overcome these problems andprovide a relatively small, less complex and more manageable method andsystem for utilizing CT's to monitor circuit branches of a load center.

FIG. 1 shows a load center 100 that includes a system for monitoringsubsidiary circuit branches 102 of the load center 100 according to oneembodiment of the current invention. The load center 100 includes ahousing 101. Within the housing 101, the load center 100 includes afirst input power line 104, a second input power line 106, a pluralityof circuit branches 102, a neutral line 108, and a ground connection110. The first and second input power lines 104, 106 are each configuredto be coupled to an external power source (e.g., a utility power system)(not shown). Each one of the plurality of circuit branches 102 isconfigured to be coupled between one of the input power lines 104, 106and an external load 112 (e.g., an appliance, a power outlet, a lightetc.). According to one embodiment, each one of the input power lines104, 106 includes a circuit breaker 113 coupled between the input powerline 104, 106 and circuit branches 102. According to another embodiment,each one of the plurality of circuit branches 102 includes a circuitbreaker 115 coupled between the input power line 104, 106 and anexternal load 112. In one embodiment, the current rating of each of thecircuit breakers 113, 115 may be configured based on the power requiredby the external load 112 to which the circuit breakers 113, 115associated circuit branch 102 is coupled. The neutral line 108 iscoupled to the ground connection 110. According to one embodiment, theneutral line is coupled to the ground connection 110 via a neutral busbar 116. According to another embodiment, the ground connection 110 iscoupled to the neutral line 108 via a ground bus bar 118.

Within the housing 101, the load center 100 also includes a plurality ofCurrent Transformers (CT) 114, a plurality of smart sensor circuits 120,a communication bus 122, and a CT concentrator 124. According to oneembodiment, the communication bus 122 includes a plurality of wires. Forexample, in one embodiment, the communication bus 122 is a ribbon cableincluding 4 wires (a power line, a return line, D+ differential pairline, D− differential pair line); however, in other embodiments, thecommunication bus 122 may include any number and type of wires. Each oneof the plurality of CT's 114 is coupled to at least one of the pluralityof circuit branches 102. According to one embodiment, CT's 114 may alsobe coupled to each input line 104, 106. According to one embodiment,each CT 114 encompasses a corresponding circuit branch 102 or input line104, 106. Each one of the plurality of CT's is also coupled to acorresponding smart sensor circuit 120. Each smart sensor circuit 120 iscoupled to the communication bus 122.

According to one embodiment, each smart sensor circuit 120 is connectedto the communication bus 122 so that each smart sensor circuit 120 is inelectrical communication with the CT concentrator 124. In oneembodiment, each smart sensor circuit 120 is clamped onto thecommunication bus 122. For example, in one embodiment, electricalcontacts (not shown) of a smart sensor circuit 120 are pressed onto thecommunication bus 122 so that the electrical contacts pierce aninsulation layer of the communication bus 122 and become electricallycoupled to appropriate conductors within the communication bus 122. Inother embodiments, the smart sensor circuits 120 may be coupleddifferently to the communication bus 122. For example, according to oneembodiment, the smart sensor circuits 120 may be coupled to thecommunication bus 122 via a bus bar or daisy chained connectors (notshown).

The connection of smart sensor circuits 120 to the communication bus 122is discussed in greater detail below.

According to one embodiment, the CT concentrator 124 includes a digitalinterface 125, at least one analog interface 127, a power module 126 anda Zigbee RF interface 128. The communication bus 122 is coupled to thedigital interface 125. The power module 126 is coupled to at least oneinput power line 104, 106 via at least one branch circuit 102. Accordingto one embodiment (not shown), at least one CT 114 is coupled directlyto at least one analog interface 127.

According to one embodiment, AC power is provided from an externalsource (e.g., a utility power system) to the input lines 104, 106. ACpower from the input lines 104, 106 is provided to each of the externalloads 112, via the circuit branches 102. The circuit breakers 113 areconfigured to automatically open and prevent current in an input line104, 106 if an overload or short circuit is detected in the input line104, 106. The circuit breakers 115 are configured to automatically openand prevent current in a circuit branch 102 if an overload or shortcircuit is detected in the circuit branch 102.

The power module 126 of the CT concentrator 124 receives AC power fromat least one input line 104, 106. Using the AC power, the power module126 powers the CT concentrator 124. In addition, the CT concentrator 124measures the AC voltage, frequency and/or phase of the AC power.According to one embodiment, the CT concentrator 124 is configured tocommunicate the measured AC voltage, frequency and/or phase informationto the smart sensor circuits 120, via the communication bus 122. Forexample, in one embodiment, the CT concentrator 124 transmits phaseinformation of the AC power to the smart sensor circuits 120 so that theCT concentrator 124 may be synchronized with the smart sensor circuits120. The synchronization of the CT concentrator 124 with the smartsensor circuits 120 will be discussed in greater detail below. Accordingto one embodiment, the CT concentrator is also capable of being poweredby a battery.

AC current passing through a circuit branch 102 or input line 104, 106induces a proportionate AC current in its associated CT 114 whichencompasses the circuit branch 102 or input line 104, 106. According toone embodiment, where a CT 114 may be coupled to multiple circuitbranches 102, an AC current proportionate to the combined current in themultiple circuit branches is induced in the CT 114 which encompasses themultiple circuit branches.

The smart sensor circuit 120 coupled to the CT 114 converts theproportionate AC current from the CT 114 into a digital value and thentransmits the digital value, over the communications bus 122 to the CTconcentrator 124. In addition, the smart sensor circuit 120 may beconfigured to utilize the voltage, frequency and/or phase informationreceived from the CT concentrator 124 over the communications bus 122.For example, in one embodiment, the smart sensor circuit 120 utilizesthe phase information received from the CT concentrator 124 tosynchronize operation with the CT concentrator 124 such that currentmeasurements performed by the smart sensor circuits 120 can bysynchronized with voltage measurements made by the CT concentrator 124.In another example, the smart sensor circuit 120 utilizes the voltage,frequency and/or phase information to calculate power and energyparameters such as RMS current, true and apparent power, and powerfactor of the circuit branch 102 or input line 104, 106. Thisinformation is also converted into digital values and sent to thedigital interface 125 of the CT concentrator 124 over the communicationsbus 122. According to one embodiment, at least one CT 114 may alsoprovide analog signals, proportionate to the AC current passing throughthe circuit branch 102, directly to an analog interface 127 of the CTconcentrator 124.

According to one embodiment, upon receiving the current information fromthe smart sensor circuits 120, the CT concentrator 124 utilizes themeasured voltage, frequency and/or phase information to calculate powerand energy parameters such as RMS current, true and apparent power, andpower factor of the circuit branch 102 or input line 104, 106.

According to one embodiment, upon receiving the current information andreceiving and/or calculating the power information, the CT concentrator124 transmits the current, power and energy information to an externalclient (e.g., a web server, in-home display, internet gateway etc.) viathe wireless Zigbee RF interface 128 to assist in power management ofthe load center 100 and to assist in power management and control of aresidence or other facility containing the system. The CT concentrator124 may also transmit the current, power and energy information to anexternal client via a wired connection or a different type of wirelessconnection.

By including a single communication bus 122 to which all smart sensorcircuits 120 are coupled, a relatively small, less complex and moremanageable method and system for utilizing a plurality of CT's 114 tomonitor circuit branches 102 of a load center 100 is provided.

FIGS. 2A and 2B illustrate one embodiment of the process of coupling aCT 114 to a circuit branch 102. According to one embodiment, a housing205 includes a CT 114 and a smart sensor circuit 120 enclosed therein.In one embodiment, a first portion 214 of the housing 205 includes a CT114 and a second portion 216 includes a smart sensor circuit 120. FIG.2A illustrates the first portion 214 prior to being coupled to a circuitbranch 102 and FIG. 2B illustrates the first portion 214 after beingcoupled to a circuit branch 102.

The first portion 214 is coupled to the second portion 216 via a hinge206. The second portion 216 includes a button 202 coupled to a lever204. Prior to the first portion 214 being coupled to the circuit branch102, the lever 114 is in an upward position, allowing the first portion214 to swing away from the second portion 216 and create an opening 208by which a circuit branch 102 may be inserted. When connection to acircuit branch 102 is desired, a user may configure the first portion214 so that the circuit branch 102 is inserted through the opening 208into an interior chamber 209. The user may then press down on the button202, causing the lever 204 to move in a downwards direction. The lever204 presses against an outside portion 210 of the first portion 214,causing the first portion 214 to swing towards the second portion 216and capture the circuit branch 102 within the interior chamber 209 ofthe first portion 214. According to other embodiments, the first portion214 may be connected to the circuit branch 102 differently. For example,the first portion 214 may be manually placed around the circuit branch102. As discussed above, after the circuit branch 102 is encompassed bythe first portion 214 (and hence also the CT 114), an AC current in thecircuit branch 102 will produce a proportionate AC current within the CT114.

FIGS. 3A, 3B and 3C illustrate the process of coupling the secondportion 216 to a communications bus 122. FIG. 3A illustrates the secondportion 216 prior to being connected to a communications bus 122. FIG.3B illustrates the second portion 216 after being connected to acommunication bus 122. FIG. 3C illustrates the second portion 216 lockedtogether with a communications bus 122. According to one embodiment, thesecond portion 216 includes an Insulation Displacement Connector (IDC)302 (e.g., an AVX series 9176 IDC). According to one embodiment, the IDC302 may include a plurality of blades 304. For example, if, as discussedabove, the second portion 216 (and hence the smart sensor circuit 120)is configured to be coupled to a four-wire ribbon cable, the IDC 302will include four blades, each blade configured to be coupled to acorresponding conductor within the cable. However, according to otherembodiments, the IDC 302 may include any number of blades to adequatelyconnect the smart sensor circuit 120 to the communications bus 122.

The second portion 216 may also include a locking lid 306 coupled to thesecond portion 216 via a hinge 308. Prior to being coupled to thecommunications bus 122, the locking lid 306 of the second portion 216 isswung away from the IDC 302, allowing a user to place the communicationbus 122 adjacent to the IDC 302. The user presses down on thecommunication bus 122, causing the communication bus 122 to pressagainst the IDC 302. The plurality of blades 304 of the IDS 302 piercethe outer insulation layer 310 of the communication bus 122, each one ofthe plurality of blades 304 connecting with a corresponding conductorwithin the communication bus 122. The user may then swing the lockinglid towards the IDC 302 and press down on the locking lid to lock thecommunication bus 122 into place. According to other embodiments, thesecond portion 216 (and hence the smart sensor circuits 120) may becoupled to the communication bus 122 in a different manner. For example,smart sensor circuits may also be coupled to the communication bus 122via a bus bar. Upon being coupled to the communication bus 122, thesmart sensor circuit 120 is in electrical communication with the CTconcentrator 124.

FIG. 4 is a circuit diagram of a plurality of CT's 114 and smart sensorcircuits 120 coupled to a communication bus 122. Each CT 114 is coupledto a circuit branch 102, or input line 104, 106, as discussed above. Forexample, in one embodiment each CT 114 is configured to encompass acircuit branch 102, or input line 104, 106, as discussed in relation toFIGS. 2A and 2B. Each smart sensor circuit 120 is coupled to acommunication bus 122 as discussed above. According to one embodiment,the communication bus 122 may be a 4-wire ribbon cable including a powerline 122 d, a D− differential pair line 122 c, a D+ differential pairline 122 b, and a return (ground) line 122 a. In one embodiment, thecommunication bus 122 is a RS-485 bus; however, according to otherembodiments, a different type of bus may be used.

Each smart sensor circuit 120 includes a microcontroller 402. In oneembodiment, the microcontroller 402 is a low power microcontroller(e.g., an STM8 low power microcontroller). According to one embodiment,the microcontroller 402 includes an analog interface 404, a referenceinterface 406, a power interface 408, a return interface 410, atransmission interface 412 and a reception interface 414. According toone embodiment, the power interface 408 is coupled to the power line 122d and the return interface 410 is coupled to the return line 122 a. Inthis way, each smart sensor circuit 120 is powered by the communicationbus 122. According to another embodiment, each CT 114 is coupled inparallel between the analog interface 404 and the reference interface406. In one embodiment, each smart sensor circuit 120 also includes aburden resistor 415 coupled in parallel between the analog interface 404and the reference interface 406.

Each smart sensor circuit 120 also includes a transceiver 403 (e.g., anRS-485 Transceiver). According to one embodiment, the transceiver 403includes a first diode 416 coupled between the transmission interface412 and the communication bus 122, and a second diode 418 coupledbetween the reception interface 414 and the communication bus 122. Also,in one embodiment, the transceiver 403 is coupled in parallel betweenthe power 122 d and return 122 a lines.

As discussed previously, AC current 416 in the circuit branch 102 orinput line 104, 106 to which a CT 114 is coupled, will produce aproportionate AC current 418 in the CT 114. The burden resistor 415converts the proportionate AC current 418 into a proportionate ACvoltage. Via the analog interface 404, the microcontroller 402 receivesthe proportionate AC voltage and converts the proportionate AC voltageinto a digital value. The microcontroller 402 then provides the digitalvalue to the transmission line 122 b via the transmission interface 412and transceiver 403, and transmits the digital value over thecommunication bus 122 to the CT concentrator 124. In addition, themicrocontroller 402 is configured to receive voltage, frequency and/orphase information from the CT concentrator 124, via the reception line122 c, the transceiver 403 and the reception interface 414. As discussedabove, the microcontroller 402 may use the additional voltage, frequencyand/or phase information received from the CT concentrator 124 alongwith the received proportionate AC current 418 to calculate power andenergy parameters of the circuit branch 102 or input line 104, 106 suchas RMS current, true and apparent power, and power factor. Thisinformation may also be converted into digital values and transmitted tothe CT concentrator 124 via the transmission interface 412, thetransceiver 403 and the transmission line 122 b. In one embodiment, themicrocontroller 402 may also use the phase information received from theCT concentrator 124 to synchronize current measurements in the smartsensor circuits 120 with voltage measurements in the CT concentrator 124

FIG. 5 is a block diagram of a CT concentrator 124. As discussed above,the CT concentrator 124 has a digital interface 125 coupled to thecommunication bus 122. The communications bus is coupled to a pluralityof smart sensor circuits 120 and a plurality of CT's 114.

According to one embodiment, the CT concentrator 124 includes a powermodule 126. In one embodiment, the power module 126 includes asingle-phase power interface 502 configured to be coupled to asingle-phase power supply. In another embodiment the power module 126includes a three-phase power interface 504 configured to be coupled to athree-phase power supply. For example, the three-phase power interface504 may be configured to receive power from a 3-phase delta or wye powerconnection. It is to be appreciated that the power supply coupled to thesingle-phase 502 or three-phase 504 interface is the same power supplycoupled to the input lines 104, 106 and as described in relation toFIG. 1. Accordingly, power received by the power module 126 issubstantially the same as power being provided to the circuit branches102.

According to one embodiment, the power module 126 also includes a DCinterface 506, a sensor interface 508 and an extra pin interface 510.According to one embodiment, the extra pin interface 510 includes fouradditional pins (e.g., a transmission pin, a reception pin, a powermodule type pin and an auxiliary power pin). However, in otherembodiments, the extra pin interface 510 may include any number and typeof pins. According to another embodiment, the CT concentrator 124 mayalso include a battery pack 512 having a DC interface 514. In oneembodiment, the power module 126 and/or battery pack 512 is modular andmay be removed from the CT concentrator 124.

According to one embodiment, the CT concentrator 124 includes a first DCinterface 516 configured to be coupled to the DC interface 514 of thebattery pack 512, a second DC interface 518 configured to coupled to theDC interface 506 of the power module 126, a sensor interface 520configured to be coupled to the sensor interface 508 of the power module126, and an extra pin interface 522 configured to be coupled to theextra pin interface 510 of the power module 126. The extra pin interface522 includes four additional pins (e.g., a transmission pin, a receptionpin, a power module type pin and an auxiliary power pin). However, inother embodiments, the extra pin interface 522 may include any numberand type of pins.

The first 516 and second 518 DC interfaces are coupled to a powermanagement module 524. The power management module 524 is coupled to amicrocontroller 528. The sensor interface 520 and the extra pininterface 522 are coupled to the microcontroller 528. The CTconcentrator 124 also includes a transceiver 530 coupled between thedigital interface 125 and the microcontroller 528 and a non-volatilememory module 532 coupled to the microcontroller 528. In one embodiment,the non-volatile memory module 532 includes Electrically ErasableProgrammable Read-Only Memory (EEPROM); however, in other embodiments,the non-volatile memory module 532 may include any type of non-volatilememory (e.g., such as serial Flash memory).

The CT concentrator 124 also includes a user interface 534 coupled tothe microcontroller. In some embodiments, the user interface may includeany type of controls which allows a user to interface with the CTconcentrator 124. (e.g., such controls include switches, buttons, LED'setc.). According to one embodiment, the CT concentrator 124 alsoincludes a USB port 536 and a serial port 538.

The CT concentrator 124 also includes a wireless radio module andantenna 540. In one embodiment, the wireless radio module is a ZigBeeradio; however, in other embodiments, the wireless radio module 540 maybe configured using a different wireless standard. According to oneembodiment, the wireless radio and antenna 540 is coupled to themicrocontroller 528, an On/Off switch 542, and a serial memory module544.

The power module 126 receives AC power from a power source (e.g., asingle-phase or three phase power source) (not shown), modulates andconverts the received AC power to DC power, and provides DC power to theCT concentrator 124 via the DC interface 506 and the second DC interface518. The power management module 524 receives the DC power from thesecond DC interface 518 and provides appropriate DC power to componentsof the CT concentrator 124 (e.g., the microcontroller 528). According toanother embodiment, the battery pack 512 may provide DC power to the CTconcentrator 124 via the DC interface 514 and the first DC interface516. The power management module 524 receives the DC power from thefirst DC interface 516 and provides appropriate DC power to componentsof the CT concentrator 124 (e.g., the microcontroller 528).

The power module 126 provides power signals received from the powersource (e.g., single-phase or three-phase source) to the microcontroller528 via the sensor interfaces 508, 520. In one embodiment, the powersignals include a voltage sense signal and a phase synchronizationsignal. According to another embodiment, the power module 126 alsoprovides additional information to the microcontroller via the extra pininterfaces 510, 522. For example, additional information may be providedto the microcontroller via a transmission pin, a reception pin, a powermodule type pin and an auxiliary power pin.

The microcontroller 528 receives the power signal information from thepower module 126, via the sensor interface 520. The microcontroller 528measures the voltage, frequency and phase of the power being provided tothe power module 126. It is to be appreciated that as the power providedto the power module 126 is substantially the same as power provided tothe circuit branches 102 (as discussed above), the voltage, frequencyand phase measured by the microcontroller 528 in relation to the powermodule 126 is the same as the voltage, frequency and phase of the powerbeing provided to the circuit branches 102.

Upon being powered, the microcontroller 528 begins to communicate withthe smart sensor circuits 120 via the transceiver 530, the digitalinterface 125 and the communication bus 122. According to oneembodiment, the microcontroller 528 may utilize the RS-485 physicalcommunication protocol to communicate over the communication bus 122.However, other physical communication protocols may be used. Themicrocontroller 528, which acts as the primary controller, identifieswhich smart sensor circuits 120 are coupled to the communication bus122. The primary microcontroller 528 treats the microcontrollers 402 assecondary controllers and assigns each secondary microcontroller 402(and hence smart sensor circuit 120) a unique address. According to oneembodiment, each time a new smart sensor circuit 120 is coupled to thecommunication bus 122, it is assigned a new address by the primarymicrocontroller 528.

According to one embodiment, the primary microcontroller 528 utilizesthe Modbus serial communication protocol to define the communication andaddressing on the communication bus 122. The primary microcontroller528, using the Modbus protocol, assigns unique addresses to the smartsensor circuits 120 and sets the structure and format of the data thatis transmitted over the communication bus 122. For example, according toone embodiment, communication over the communication bus 122 using theModbus protocol may be performed as described in U.S. patent applicationSer. No. 13/089,686 entitled “SYSTEM AND METHOD FOR TRANSFERRING DATA INA MULTI-DROP NETWORK”, filed on Apr. 19, 2011, which is hereinincorporated by reference in its entirety. In one embodiment, theprimary microcontroller 528 utilizes an auto addressing scheme. Forexample, the primary microcontroller 528 utilizes an auto addressingscheme as described in U.S. patent application Ser. No. 13/089,678entitled “SYSTEM AND METHOD FOR AUTOMATICALLY ADDRESSING DEVICES IN AMULTI-DROP NETWORK”, filed on Apr. 19, 2011, which is hereinincorporated by reference in its entirety.

According to one embodiment, the Modbus protocol allows for up to 255smart sensor circuits 120 to be simultaneously attached to thecommunication bus 122. It also is to be appreciated that the number ofsmart sensor circuits 120 may be limited by the load center 100 itself.For example, in common residential load centers, the maximum number ofbranch circuits (and hence smart sensor circuits) is seventy-two.However, according to at least one embodiment, different communicationprotocols may be used by the primary 528 and secondary 402microcontrollers to allow any number of smart sensor circuits 120 to becoupled to the communication bus 122 (e.g., for use in large, commercialload centers).

According to one embodiment, once all of the smart sensor circuits 120have been identified and assigned addresses by the primarymicrocontroller 528, a user, via the user interface 534, may associateeach smart sensor circuit 120 with a specific load (e.g., sensor #12 isassigned to an air conditioner; sensor #13 is assigned to aRefrigerator, etc.).

Once the identification and addressing of the smart sensor circuits 120is complete, the primary microcontroller 528 monitors the smart sensorcircuits 120. The primary microcontroller 528 determines which smartsensor circuits 120 are attempting to communicate over the communicationbus 122 and controls communication on the bus 122 to eliminate conflictsor data collision. In addition, according to one embodiment, the primarymicrocontroller 528 provides power parameter information to the smartsensor circuits 120. For example, as discussed above, the primarymicrocontroller 528 measures the voltage, frequency and phase of thepower being provided to the power module 126 (and hence the circuitbranches 102). When needed by a smart sensor circuit 120, the primarymicrocontroller 528 transmits the parameter information to the smartsensor circuit 120, via the transceiver 530 and communication bus 122.

As discussed above, each smart sensor circuit 120 measures the currentthrough an associated circuit branch 102 or input line 104, 106.According to one embodiment, using the measured current and the receivedadditional parameter (e.g., voltage, frequency and phase) informationfrom the primary microcontroller 528, a smart sensor circuit 120calculates power information such as RMS current, true and apparentpower, and power factor of the associated circuit branch 102 or inputline 104, 106. The calculated current and/or power information istransmitted to the primary microcontroller 528, via the communicationbus 122, digital interface 125, and transceiver 530. In one embodiment,the power information is transmitted to the primary microcontroller 528at a time and rate determined by the microcontroller 528. As discussedabove, according to one embodiment, the primary microcontroller 528 mayalso receive analog current information directly from a CT 114, via ananalog interface 127.

According to one embodiment, upon receiving the calculated current fromthe smart sensor circuits 120, the primary microcontroller 528 utilizesthe measured voltage, frequency and/or phase information to calculatepower and energy parameters such as RMS current, true and apparentpower, and power factor of the circuit branch 102 or input line 104,106.

The current, power and energy information is provided to the wirelessradio module and antenna 540 by the primary microcontroller 528. Thewireless radio module and antenna 540 wirelessly transmits the current,power and energy information to an external client (e.g., a web server,in-home display, or internet gateway) to provide electric power andenergy consumption data to end users or other interested parties.According to one embodiment, the current, power and energy informationmay also be provided to an external client through a wired connection(e.g., via the USB port 536 or serial port 538). According to anotherembodiment, the current, power and energy information may be provided toan external client through another type of interface, such as enEthernet or Power Line Communication (PLC) port (not shown).

In one embodiment described above, each smart sensor circuit 120determines power information for its associated branch circuit andtransmits the information to the CT concentrator 124. In anotherembodiment, which will now be described with reference to FIG. 6, the CTconcentrator 124 synchronizes current measurements by each smart sensorcircuit 120 with voltage measurements performed by the CT concentrator124. This allows the CT concentrator 124 to calculate power informationbased only on current information received from the smart sensorcircuits 120.

FIG. 6 is a flow chart of a method of operation of the CT concentrator124 of FIG. 5, according to one embodiment. At block 602, the CTconcentrator 124, and hence the smart sensor circuits 120, are poweredup. At block 604, the primary microcontroller 528 of the CT concentratorassigns unique addresses to each smart sensor circuit 120, via thecommunications bus 122. According to one embodiment, the primarymicrocontroller 528 utilizes an auto addressing scheme, as discussedabove. At block 606, the primary microcontroller 528 broadcastsparameter information to each smart sensor circuit 120, via thecommunication bus 122. According to one embodiment, the parameterinformation includes at least one of frequency (or period), the numberof samples per period, and a defined sleep timer. In another embodiment,the broadcast information includes scaling parameters. According toanother embodiment, the broadcast information includes previous cyclecomputation results (e.g., for RMS current, power, energy).

At block 608, the primary microcontroller 528 requests each smart sensorcircuit 120 to acknowledge the receipt of the broadcast information viathe communication bus 122. According to one embodiment, at block 608,the primary microcontroller 528 also requests that each smart sensorcircuit 120 transmit its sensor type (e.g., 20 A, 80 A, or 200 A currenttransformer) to the primary microcontroller 528 via the communicationbus 122. At block 610, the primary microcontroller 528 creates aninventory of all of the sensor circuits 120 and their type (e.g., bymodel number). At block 612, the primary microcontroller 528 transmitsto each smart sensor circuit 120 that the smart sensor circuit 120should enter power save mode.

According to one embodiment, once a smart sensor 120 enters power savemode, a sleep timer is enabled. In one embodiment, the use of the sleeptimer is intended to limit the overall power consumption of the system.For example, in one embodiment, when a smart sensor 120 is in power savemode, the smart sensor 120 will not communicate on the communicationbus, and hence will require a lower level of power, until the sleeptimer has expired. By placing at least a portion of the smart sensors120 in power save mode, the total number of smart sensors 120 requiringfull power is limited and the total power consumption of the system maybe reduced. According to one embodiment, the sleep timer isprogrammable. In one embodiment, the sleep timer is configured with atime equal to slightly less than the total number of smart sensors 120multiplied by the period over which current is to be sampled.

For example, according to on embodiment, the sleep timer is configuredwith a time (T) calculated with the following formula:

T=(s−2)*t+(t/2);

where:

s represents the total number of smart sensors 120, and

t represents the sample period defined by the primary microcontroller528.

In one example, where the sample period is 20 ms and the system includesa total of 6 smart sensors 120, the time T is calculated as 90 ms. Inthis example, after a smart sensor 120 has conducted measurements andfinished transmitting current sample raw data, it will enter power savemode for 90 ms and will not sample current again until time T (90 ms)has expired. However, in other embodiments, the sleep timer may beconfigured differently.

In one embodiment, smart sensors 120 currently in power save mode areconfigured to exit power save mode early (i.e., before the expiration oftime T), to prepare for current sampling which will begin upon theexpiration of time T. For example, in one embodiment, smart sensors 120currently in power save mode are configured to exit power save mode 10ms early. In such an embodiment, the total time each smart sensor 120will be awake is 30 ms (20 ms period in addition to 10 ms awakeningperiod). Hence, by staggering the current sampling performed by thesmart sensors 120, the number of smart sensors 120 requiring power atthe same time is limited and as a result, the total power consumption ofthe system is reduced. This is particularly useful for battery operatedsystems.

At block 614, the primary microcontroller 528 senses the voltage,frequency and/or phase of the power signal information received from thepower module 126 via the sensor interface 520. For example, according toone embodiment, the primary microcontroller 528 senses voltage and/orfrequency through a voltage sense signal and the primary microcontroller528 senses phase through a phase synchronization signal. As discussedabove, according to some embodiments, the power signal informationreceived from the power module 126 may be correlated to single, doubleor 3-phase power.

At block 616, the primary microcontroller 528 computes the RMS voltagefor all phases that are present (e.g., 1, 2, or 3). Also at block 616,the primary microcontroller 528 compares the RMS voltage to the primarymicrocontroller's 528 nominal voltage to confirm that the RMS voltageand phase signal(s) are correct. For example, according to oneembodiment, if the primary microcontroller 528 is connected to a utilitysystem in North America, the primary microcontroller 528 will confirmthat it is measuring a 120V, 60 Hz signal. However, in anotherembodiment, if the primary microcontroller 528 is connected to a utilitysystem in Europe, the primary microcontroller 528 will confirm that itis measuring a 220V, 50 Hz signal.

At block 618, the primary microcontroller 528 determines the appropriatephase angle at which synchronized measurements will be taken. Accordingto one embodiment, the phase angle may be configured as any phase angle,and does not have to be limited to a zero crossing. In some embodiments,the phase angle may be configured at an angle other than at a zerocrossing to intentionally avoid noise which may exist at the zerocrossing.

At blocks 620 and 622, synchronized sampling by the primarymicrocontroller 529 and the smart sensor circuits 120 begins at thepreviously determined phase angle. For example, according to oneembodiment, at block 620, the primary microcontroller 528 communicatesto all of the smart sensor circuits 120 simultaneously to start samplingcurrent in their respective circuit branches 102 at the predeterminedphase angle. Also, at the same time as block 620, the primarymicrocontroller 528 at block 622 initiates voltage sampling of the powersignal information received from the power module 126 at the previouslydetermined phase angle to synchronize the voltage measurements with thecurrent measurements made by all of the smart sensor circuits 120.According to one embodiment, the primary microcontroller 528 samplesvoltage over the same period of time in which the smart sensor circuits120 sample current.

According to another embodiment, instead of communicating to all of thesmart sensor circuits 120 simultaneously, the primary microcontroller528 communicates to at least one specific sensor (e.g., a sensor havinga unique address) to begin sampling current in the respective circuitbranch 102. In this way, the primary microcontroller 528 is able tostart sampling current in at least one specific type of circuit branch(e.g., a circuit branch coupled to a specific type of load). By onlysampling current in a select number of circuit branches 102, the overallpower consumption of the system may be reduced.

According to one embodiment, each smart sensor circuit 120 which iscontrolled to begin sampling will sample current in the smart sensorcircuits 120 respective branch over a predefined period of time for apredefined number of samples, the time and number of samples beingpreviously set by the primary microcontroller 528 in the broadcastparameter information. In one embodiment, the current sampling raw datais stored in a buffer of each smart sensor circuit 120.

At block 624, upon completing voltage sampling for the given period, theprimary microcontroller 528 requests that each smart sensor circuit thatwas sampling current, transmit the current sampling raw data for thegiven time period from the buffer to the primary microcontroller 528 viathe communication bus 122. According to one embodiment, the currentsampling raw data is time-stamped.

At block 626, upon confirming receipt of the current sampling raw data,the primary microcontroller 528 broadcasts to the previous currentsampling smart sensors 120 that the smart sensors 120 should enter powersave mode, making more power available for other smart sensors (asdiscussed above).

According to one embodiment, at block 626, using the received currentdata and measured voltage data, the primary microcontroller 528calculates the RMS current, power (e.g., 4 quadrant) and/or energy usageof the circuit branches 102 associated with the smart sensors 102 fromwhich the primary microcontroller 528 received the raw current samplingdata. According to one embodiment, the primary microcontroller 528 mayautomatically take into account any communication delay between theprimary microcontroller 528 and the smart sensors 102 when making itscurrent, power and/or energy calculations. After calculating thecurrent, power and energy information, the primary microcontroller 528may repeat blocks 620 to 628 for another smart sensor 120 or group ofsmart sensors 120.

In at least some embodiments, the use of the primary microcontroller 528to individually control the synchronization of the smart sensor circuits120, eliminates any need to individually wire each smart sensor circuit120 with phase synchronization signals from the power module. PhaseLocked Loop (PLL) circuitry within the smart sensor circuits 120 mayalso be eliminated, as the primary microcontroller 528 will control thesynchronization. By allowing the primary microcontroller 528 to selectthe phase angle at which sampling will occur, the flexibility of thesystem may be increased. For example, any appropriate phase angle may beselected to provide the most desirable results.

Even though examples in accordance with the present invention aredescribed herein in reference to a load center, other examples may beutilized within any electrical system in which current, power and energyof a power line are desired to be monitored. It also is to beappreciated that examples in accordance with the present invention maybe utilized to monitor any type (e.g., commercial or residential) orsize system.

Even though examples in accordance with the present invention aredescribed herein as utilizing a current transformer 114 capable of beingclamped onto a circuit branch 102, other examples may utilize adifferent type of current sensor. For example, current sensors utilizingshunt resistance, hall-effect, and toroidal (solid core) currenttransformers may be used.

In at least some examples in accordance with the present inventiondescribed herein communication between the sensor circuits 120 and theCT concentrator 124 is conducted over a wired interface (i.e. thecommunication bus 122). Other examples may utilize a wireless interface.For example, communication between the sensor circuits 120 and the CTconcentrator 124 may be performed in compliance with a wireless standardsuch as the ZigBee RF4CE standard or the IEEE 802.15 standard asdescribed in U.S. patent application Ser. No. 12/789,922 entitled“SYSTEM FOR SELF-POWERED, WIRELESS MONITORING OF ELECTRICAL CURRENT,POWER AND ENERGY”, filed on May 28, 2010, which is herein incorporatedby reference in its entirety.

By including only a single communication bus within a load center,rather than individual dedicated connections (e.g., “hub and spokewiring”), and connecting all smart CT's to a CT concentrator within theload center via the single communication bus; a relatively small, lesscomplex and more manageable method and system for utilizing a pluralityof CT's to monitor circuit branches of a load center is provided.

Having thus described several aspects of at least one embodiment of thisinvention, it is to be appreciated various alterations, modifications,and improvements will readily occur to those skilled in the art. Suchalterations, modifications, and improvements are intended to be part ofthis disclosure, and are intended to be within the spirit and scope ofthe invention. Accordingly, the foregoing description and drawings areby way of example only.

1. A system for monitoring a plurality of circuit branches coupled to aninput line, the system comprising: a communication bus; a plurality ofsensor circuits, each configured to be coupled to the communication busand at least one of the plurality of circuit branches, wherein eachsensor circuit is further configured to sample current in the at leastone of the plurality of circuit branches; a controller configured to becoupled to the communication bus and the input line; wherein thecontroller is further configured to sample voltage on the input line;and wherein the controller is further configured to synchronize, via thecommunication bus, current sampling performed by the plurality of sensorcircuits with the voltage sampling performed by the controller.
 2. Thesystem of claim 1, wherein the controller is further configured toreceive, via the communication bus, current sampling data from at leastone of the plurality of sensor circuits.
 3. The system of claim 2,wherein the controller is further configured to calculate at least oneof RMS current, power, or energy usage of at least one of the pluralityof circuit branches based on the current sampling data received from theat least one of the plurality of sensor circuits and voltage samplingdata.
 4. The system of claim 1, wherein the controller is furtherconfigured to determine a phase angle of a voltage waveform at whichcurrent sampling and voltage sampling should occur.
 5. The system ofclaim 1, wherein at least one of the plurality of sensor circuitsincludes a current transformer coupled to the at least one of theplurality of circuit branches.
 6. A method for monitoring a plurality ofcircuit branches coupled to a power line, the method comprising:coupling a sensor circuit to each one of the plurality of circuitbranches and to a communication bus; coupling a controller to thecommunication bus and to the power line; sampling, with at least one ofthe sensor circuits, current in at least one of the plurality of circuitbranches; sampling, with the controller, voltage on the power line; andsynchronizing, with the controller via the communication bus, thesampling of current by the at least one of the sensor circuits and thesampling of voltage by the controller.
 7. The method of claim 6, whereinthe act of synchronizing comprises: detecting, by the controller, avoltage waveform on the power line; and determining, with thecontroller, a phase angle of the voltage waveform at which the acts ofsampling current and sampling voltage should occur.
 8. The method ofclaim 7, wherein the act of synchronizing further comprises:broadcasting, with the controller via the communication bus, to each oneof the sensor circuits that the act of sampling current should begin;and initiating, after a predetermined delay following the act ofbroadcasting, the act of sampling voltage.
 9. The method of claim 7,wherein the act of synchronizing further comprises: broadcasting, withthe controller via the communication bus, to at least one of the sensorcircuits that the act of sampling current should begin; and initiating,after a predetermined delay following the act of broadcasting, the actof sampling voltage.
 10. The method of claim 6, further comprisingreceiving, with the controller via the communication bus, currentsampling data from at least one of the sensor circuits.
 11. The methodof claim 10, further comprising transmitting the current sampling datato an external client.
 12. The method of claim 10, further comprisingcalculating, with the controller, at least one of RMS current, voltageor energy usage of at least one of the plurality of circuit branchesbased on the current sampling data received from the at least one of thesensor circuits and voltage sampling data.
 13. The method of claim 12,further comprising transmitting the at least one of RMS current, voltageor energy usage to an external client.
 14. The method of claim 13,wherein the act of transmitting includes transmitting the at least oneof RMS current, voltage or energy usage wirelessly to an externalclient.
 15. The method of claim 10, further comprising: confirming, withthe controller in response to the act of receiving current samplingdata, that the current sampling data was received successfully; andentering, with the at least one of the sensor circuits, in response tothe act of confirming, power save mode.
 16. The method of claim 13,wherein the act of entering power save mode comprises initiating a sleeptimer, wherein the at least one of the sensor circuits remains in powersave mode until expiration of the sleep timer.
 17. The method of claim6, further comprising assigning, with the controller via thecommunication bus, unique addresses to each one of the sensor circuits.18. A system for monitoring a plurality of circuit branches coupled toan input line, the system comprising: a communication bus; a pluralityof sensor circuits, each configured to be coupled to the communicationbus and at least one of the plurality of circuit branches, wherein eachsensor circuit is further configured to sample current in the at leastone of the plurality of circuit branches; a controller configured to becoupled to the communication bus and the input line; means forsynchronizing current sampling performed by at least one of theplurality of sensor circuits and voltage sampling performed by thecontroller.
 19. The system of claim 18, wherein the controller isfurther configured to receive, via the communication bus, currentsampling data from the at least one of the plurality of sensor circuit.20. The system of claim 19, wherein the controller is further configuredto calculate at least one of RMS current, power, or energy usage of atleast one of the plurality of circuit branches based on the currentsampling data received from the at least one of the plurality of sensorcircuit and voltage sampling data.